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1 /* @(#)s_cos.c 5.1 93/09/24 */
2 /*
3  * ====================================================
4  * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
5  *
6  * Developed at SunPro, a Sun Microsystems, Inc. business.
7  * Permission to use, copy, modify, and distribute this
8  * software is freely granted, provided that this notice
9  * is preserved.
10  * ====================================================
11  */
12 #include  <LibConfig.h>
13 #include  <sys/EfiCdefs.h>
14 #if defined(LIBM_SCCS) && !defined(lint)
15 __RCSID("$NetBSD: s_cos.c,v 1.10 2002/05/26 22:01:54 wiz Exp $");
16 #endif
17 
18 /* cos(x)
19  * Return cosine function of x.
20  *
21  * kernel function:
22  *  __kernel_sin    ... sine function on [-pi/4,pi/4]
23  *  __kernel_cos    ... cosine function on [-pi/4,pi/4]
24  *  __ieee754_rem_pio2  ... argument reduction routine
25  *
26  * Method.
27  *      Let S,C and T denote the sin, cos and tan respectively on
28  *  [-PI/4, +PI/4]. Reduce the argument x to y1+y2 = x-k*pi/2
29  *  in [-pi/4 , +pi/4], and let n = k mod 4.
30  *  We have
31  *
32  *          n        sin(x)      cos(x)        tan(x)
33  *     ----------------------------------------------------------
34  *      0        S     C     T
35  *      1        C    -S    -1/T
36  *      2       -S    -C     T
37  *      3       -C     S    -1/T
38  *     ----------------------------------------------------------
39  *
40  * Special cases:
41  *      Let trig be any of sin, cos, or tan.
42  *      trig(+-INF)  is NaN, with signals;
43  *      trig(NaN)    is that NaN;
44  *
45  * Accuracy:
46  *  TRIG(x) returns trig(x) nearly rounded
47  */
48 
49 #include "math.h"
50 #include "math_private.h"
51 
52 double
cos(double x)53 cos(double x)
54 {
55   double y[2],z=0.0;
56   int32_t n, ix;
57 
58     /* High word of x. */
59   GET_HIGH_WORD(ix,x);
60 
61     /* |x| ~< pi/4 */
62   ix &= 0x7fffffff;
63   if(ix <= 0x3fe921fb) return __kernel_cos(x,z);
64 
65     /* cos(Inf or NaN) is NaN */
66   else if (ix>=0x7ff00000) return x-x;
67 
68     /* argument reduction needed */
69   else {
70       n = __ieee754_rem_pio2(x,y);
71       switch(n&3) {
72     case 0: return  __kernel_cos(y[0],y[1]);
73     case 1: return -__kernel_sin(y[0],y[1],1);
74     case 2: return -__kernel_cos(y[0],y[1]);
75     default:
76             return  __kernel_sin(y[0],y[1],1);
77       }
78   }
79 }
80